src/main/java/eu/svjatoslav/sixth/data/store/file/MetaData.java

   1 /*
   2  * Sixth - System for data storage, computation, exploration and interaction.
   3  * Copyright ©2012-2016, Svjatoslav Agejenko, svjatoslav@svjatoslav.eu
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of version 3 of the GNU Lesser General Public License
   7  * or later as published by the Free Software Foundation.
   8  */
   9
  10 package eu.svjatoslav.sixth.data.store.file;
  11
  12 import java.io.IOException;
  13
  14 public class MetaData {
  15
  16     public static final int FILE_LOCATION_ENTRY_ALLOCATION_TABLE_START = 4 * 6;
  17     private static final int FORMAT_VERSION = 1;
  18     private static final int FILE_LOCATION_VERSION = 4 * 0;
  19     private static final int FILE_LOCATION_ENTRIES_TABLE_SIZE = 4 * 1;
  20     private static final int FILE_LOCATION_USED_ENTRIES_COUNT = 4 * 2;
  21     private static final int FILE_LOCATION_CURRENT_ENTRY = 4 * 3;
  22     private static final int FILE_LOCATION_CURRENT_LOCATION = 4 * 4; // LONG!!
  23     private final FileDataStore dataStore;
  24     private int entriesTableSize;
  25     private int currentEntry;
  26     private int usedEntriesCount;
  27     private long currentLocation;
  28
  29     public MetaData(final FileDataStore dataStore) {
  30         this.dataStore = dataStore;
  31     }
  32
  33     /**
  34      * @return address of the start of the allocated space
  35      */
  36     public synchronized long allocateStorageSpace(final int amountOfBytes) {
  37         final long locationStart = currentLocation;
  38         currentLocation += amountOfBytes;
  39         return locationStart;
  40     }
  41
  42     public void decreaseUsedEntriesCount() {
  43         usedEntriesCount--;
  44     }
  45
  46     public synchronized void ensureMinimumCurrentLocation(
  47             final long minimumLocation) {
  48
  49         if (currentLocation < minimumLocation)
  50             currentLocation = minimumLocation;
  51     }
  52
  53     public boolean entriesTableNeedsIncreasing() {
  54         final int reserveSize = (entriesTableSize / 10) + 1;
  55
  56         return usedEntriesCount >= (entriesTableSize - reserveSize);
  57
  58     }
  59
  60     public long getEntriesStorageAreaStart() {
  61         return FILE_LOCATION_ENTRY_ALLOCATION_TABLE_START
  62                 + (EntryRecord.ENTRY_RECORD_LENGTH * entriesTableSize);
  63     }
  64
  65     public long getEntriesStorageAreaStart(
  66             final int hypotheticalEntriesTableSize) {
  67         return FILE_LOCATION_ENTRY_ALLOCATION_TABLE_START
  68                 + (EntryRecord.ENTRY_RECORD_LENGTH * hypotheticalEntriesTableSize);
  69     }
  70
  71     /**
  72      * @return amount of entries in the entries table
  73      */
  74     public int getEntriesTableSize() {
  75         return entriesTableSize;
  76     }
  77
  78     public void setEntriesTableSize(final int newSize) {
  79         entriesTableSize = newSize;
  80     }
  81
  82     public int getNewEntryId() {
  83         currentEntry++;
  84
  85         if (currentEntry >= getEntriesTableSize())
  86             currentEntry = 0;
  87
  88         return currentEntry;
  89     }
  90
  91     public void increaseUsedEntriesCount() {
  92         usedEntriesCount++;
  93     }
  94
  95     public void initializeNewFile() throws IOException {
  96         entriesTableSize = 16;
  97         usedEntriesCount = 0;
  98         currentEntry = entriesTableSize - 1;
  99         currentLocation = getEntriesStorageAreaStart();
 100
 101         writeFileHeader();
 102     }
 103
 104     public void readFileHeader() throws IOException {
 105
 106         final int fileVersion = dataStore.readInt(FILE_LOCATION_VERSION);
 107         if (fileVersion != FORMAT_VERSION)
 108             throw new RuntimeException("File version is " + fileVersion
 109                     + " but version " + FORMAT_VERSION + " is required.");
 110
 111         entriesTableSize = dataStore.readInt(FILE_LOCATION_ENTRIES_TABLE_SIZE);
 112
 113         usedEntriesCount = dataStore.readInt(FILE_LOCATION_USED_ENTRIES_COUNT);
 114
 115         currentEntry = dataStore.readInt(FILE_LOCATION_CURRENT_ENTRY);
 116
 117         currentLocation = dataStore.readLong(FILE_LOCATION_CURRENT_LOCATION);
 118     }
 119
 120     public void setCurrentLocation(final long currentLocation) {
 121         this.currentLocation = currentLocation;
 122     }
 123
 124     public void writeFileHeader() throws IOException {
 125         dataStore.writeInt(FILE_LOCATION_VERSION, FORMAT_VERSION);
 126         dataStore.writeInt(FILE_LOCATION_ENTRIES_TABLE_SIZE,
 127                 getEntriesTableSize());
 128         dataStore.writeInt(FILE_LOCATION_USED_ENTRIES_COUNT, usedEntriesCount);
 129         dataStore.writeInt(FILE_LOCATION_CURRENT_ENTRY, currentEntry);
 130         dataStore.writeLong(FILE_LOCATION_CURRENT_LOCATION, currentLocation);
 131     }
 132
 133 }